The present invention relates to a tension measuring device, and particularly, but not exclusively, relates to a tension measuring device for graft fixation, for example, tendon or ligament fixation.
Due to increasing involvement of people with active sport, injuries are becoming increasingly common where tissues such as ligaments or tendons tear or detach from bone. Surgical techniques have been developed to reconstruct such soft tissues and to re-attach them to the relevant bone. Some of the most common types of such injuries are tearing of the anterior or posterior cruciate ligament (ACL or PCL). Reconstruction of such tissues generally involves replacement with a graft such as autologous or artificial tendon. An autologous tendon graft may be taken from the patients patella tendon or, alternatively, the Semi-tendinosus or Semitendinosus/Gracilis may be utilised.
A particularly important issue in these and other grafting operations is that the graft is fixed in the bone tunnel at the required and at a reproducible tension.
Therefore, in an attempt to improve the quality and consistency of arthroscopic ACL or PCL replacement, surgeons are paying more attention to the level of pre-tensioning applied to the graft prior to it being locked in place. The ultimate goal is to place the graft into the knee joint and lock it at a tension which accurately replicates the normal cruciate ligament of the patient. U.S. Pat. No. 5,713,897 describes an ACL tensioning device which maintains a required tensile stress on the distal end of a cruciate ligament graft fixed in the femoral tunnel section, and for maintaining that applied tensile stress as the ligament is mounted in or onto the tibia. However, this and other current methods of tensioning the distal end of the graft below the tibial tunnel are somewhat without justification as there is no way of measuring the tension of a normal ACL at its distal point. An applied force at this point could be said to be irrelevant, as there is no standard to compare against.
With a view to addressing the problems of the prior art mentioned above, or otherwise, it is one of the aims of at least preferred embodiments of the present invention to provide a device which, instead of applying a known tension to the distal end of the graft, measures the resultant effect that the tension applied at this point has on the graft in the joint.
According to a first aspect of the present invention, there is provided a tension measuring device suitable for measuring the tension of soft tissue attached to bone, the device comprising a body region, force applying means extending from said body and operable to apply a translational force to soft tissue attached to bone, and abutment means extending from said body and operable to abut, in use, a bone to which the soft tissue is attached, the abutment means being responsive to the application of translational movement to the force applying means to thereby measure the applied translational movement and the force applying means being responsive to the tension in the soft tissue to transfer said applied translational movement to the soft tissue below a predetermined soft-tissue tension and to extend above the said pre-determined tension to prevent further translation of the soft tissue.
Preferably, the extension of the force applying means is measured by suitable measuring means such as an associated translation scale.
Preferably, the force applying means is resiliently longitudinally deformable. Preferably, the abutment means is resiliently longitudinally deformable. Preferably, the abutment means distal end is biased, preferably, longitudinally biased, towards the bone, in use, to remain in contact therewith during the application of translational movement away from the bone. Preferably, the force applying means is under a fixed tension with respect to elongation thereof. Preferably, the fixed tension is applied by means of a tension spring which engages the force applying means to prevent elongation below a pre-determined applied force.
Preferably, the device measures the tension in the soft tissue by determining the extent of the translational movement of the soft tissue in response to the force applying means.
Advantageously, instead of applying a known force to the distal end of the soft tissue, the device measures the effect the applied force has on the soft tissue and thereby the tension in the soft tissue. Preferably, the device is used to measure the tension of the soft tissue which is attached to the bone by both the proximal and distal ends of said soft tissue.
Preferably, the force applying means and the abutment means extend outwardly in the same direction from the body region. Preferably, the force applying means and the abutment means are, preferably, spaced from each other and, preferably, substantially parallel to one another.
Preferably, the abutment means is operable to abut the anterior surface of a tibia bone, more preferably, the proximal anterior surface of the said bone. Preferably, the abutment means comprises an elongate shaft with, preferably, spike means at the distal end thereof, the spike means being operable to make a firm contact with the bone. Preferably, the abutment means comprises resilient means which urges the elongate shaft into abutment with the bone. The resilient means may be a compression spring which engages a proximal part of the abutment means to urge it into abutting contact with the bone.
The abutment means may further comprise locking means to lock the abutment means in a retracted position. The locking means may be released thereby urging the abutment means outwards towards the bone. Preferably, the abutment means comprises suitable translation measuring means, preferably, a translation scale on which the applied translational movement, typically, translation of the body region with respect to the bone may be measured. The translation scale may be located within the body region at the proximal end of the abutment means to that of the bone abutting end.
The translation scale may be analogue or digital.
Preferably, the force applying means is a pulling means which is placed, preferably, in direct contact with the soft tissue to which the translation force is to be applied. Preferably, the pulling means is adapted at its distal end to abut at least part of the rearwardly facing side of the soft tissue with respect to the body of the device. Preferably, the pulling means comprises a hooking means which is hookable around the soft tissue. Preferably, the pulling means comprises an elongate shaft which has hooking means at the distal end thereof. Preferably, the hooking means is hooked around the rear of the soft tissue and arranged to apply translational force to the soft tissue in the required direction.
Preferably, the pulling means comprises resilient means which is arranged to apply a pre-determined force to the soft tissue resulting from the translational movement applied to the tissue by the user. The resilient means may be associated with the pulling means and may be a spring, preferably a tension spring which, preferably, engages at least part of the pulling means.
Preferably, the force applying means is associated with a translation scale by which the elongation of the force applying means and thereby the tissue may be measured. The translational movement in the tissue is determined by subtracting the elongation of the force applying means from the applied translational movement. The translation scale may be located within the body region of the device. The translation scale may be analogue or digital and may measure the extent of the movement of the soft tissue under a specific force of the resilient means and this may be measured in appropriate units. Preferably, a tension spring at a pre-determined tension is used in engagement with the force applying means.
The pulling means may comprise adjustment means to adjust the resilience or pre-determined tension of the pulling means.
The device may be used to measure the tension of any soft tissue attached to any bone. Preferably, the device is used for measuring the tension of a ligament in a joint where a known tension needs to be applied to the ligament. Most preferably, the device is used to measure the tension of anterior cruciate ligaments (ACL) . The device may be used to measure the tension of an ACL in a healthy individual. Alternatively, or additionally, the device may be used to reproduce this reference tension in a reconstructed graft such as an ACL.
According to a second aspect of the present invention, there is provided a method of measuring the tension of soft tissue attached to at least one bone comprising applying a translational movement under a pre-determined force to the tissue using a force applying means on a device according to the first aspect of the invention to thereby cause a measurable translational movement of the tissue with respect to the said at least one bone.
The method may comprise one or more of the steps of:
(i) introducing the force applying means to the soft tissue;
(ii) urging the abutment means against at least one bone in contact with the said soft tissue; and
(iii) applying the force to the soft tissue such that the translational movement is in the direction required.
Preferably, the translational movement applied and the elongation of the force applying means is measured and, it is from these that the tension of the soft tissue is determined. Preferably, the translational movement of the soft tissue is measured by subtracting the elongation of the force applying means from the translational movement applied.
The force applying means may be introduced to the soft tissue through an aperture in a patient being treated. Preferably, the aperture is an arthroscopic portal. Preferably, the force applying means comprises an elongate shaft and hooking means at the distal end thereof. Preferably, the hooking means is hooked around the rear of the soft tissue and is arranged to apply translational force to the soft tissue in the required direction.
The method of the second aspect may utilise any one or any combination of features of the first aspect or the preferred features of the first aspect.
The locking means may be operable to lock the abutment means in at least one position. The abutment means may be pulled proximally in a first direction and the locking means is operable to lock the now retracted abutment means at a first position. The locking means may be released to allow the abutment means to be urged distally from the first retracted position to an un-retracted, second position under the resilient force of the compression spring. The position of the abutment means, when in a retracted position, may be variable and determined by the operator.
The method may further comprise the step of:
(i) releasing the locking means such that the abutment means is urged against the tibia.
Preferably, the translation force is applied to the soft tissue via the force applying means by moving the body of the device away from the soft tissue whilst the abutment means remains in contact with the bone. Preferably, the force applied by the force applying means is pre-determined. Preferably, the force applying means comprises a scale from which the translation of the force applying means may be measured. Preferably, the abutment means and force applying means comprise scales from which the translation of the soft tissue may be calculated. Preferably, the degree of translation of the soft tissue is determined by reading off a measurement on the abutment translation scale and subtracting the measurement read off the force translation scale. Preferably, the abutment translation scale moves in response to a compression spring as the body of the device is moved away from the bone and, preferably, the force applied translation scale is moved in response to elongation of the force applying means in response to the tension in the soft tissue.
The method may be used to measure the tension of any soft tissue attached to any bone. Preferably, the method is used for measuring the tension of a ligament in a joint where a known tension needs to be applied to the ligament. Most preferably, the method is used to measure the tension of anterior cruciate ligaments (ACL). The method may be used to determine the tension of an ACL in a healthy individual. Preferably, routine arthroscopies are carried out in order to obtain an average value of the tension in the ACL of healthy individuals. Alternatively, or additionally, the method may be used to reproduce this reference tension in a reconstructed graft ACL. Once an average value of the tension of normal healthy ACLs has been obtained, a surgeon may then aim to reproduce this by tensioning the distal end of a graft ACL and measuring the translation of this ACL. Preferably, this is repeated until the reference translation is achieved in the joint, at which time the ACL may be locked in place either immediately or, preferably, following cycling of the joint and re-checking the tension in case any stretch of tissues or proximal fixation slippage has occurred. It is not necessary to apply excessive force to the normal or graft ACL to achieve accurate results since applying the same force time after time is the key to reproducibility.
It should be further noted that although the above example refers to ACL fixation, this invention is not limited to this application and it will be clear to the skilled technician that the device has numerous applications in connection with the replacement of any ligaments in the human or animal body.
All of the features disclosed herein may be combined with any of the above aspects in any combination.